vessy

As post states, been doing this for a while but i've kind of eliminated everything.

New coil packs, checked plugs, gapped at 0.7, new ignitor, new crank and cam sensors, earths checked.

I changed the plugs (6B's) when i got the car so i can't be sure if it did it with the old plugs, however they all looked fine. Misfire happens above 6k everytime, sometimes the rev needle jumps around. Could the plugs be getting too hot and breaking down? Should i be running 7's?

car is MY95, ESL chip, complete de-cat and panel filter, this problem was apparent before ESL went in.

Any ideas?

jonnyh

Fuel pump.....?

Rokay

7b's............used on jdms and tweeked cars. Worth a try if you think your 6's are not up to scratch.

Panel filter.........trust it's a dry one and not an oil impregnated filter. Try a Green cotton if you haven't done so all ready. Clean the maf as well.

While your there might as well clean the boost solenoid as well and chk sense lines.

ESL

Try the gaps at 0.6mm and then 0.5mm to see if that has any effect. Does it throw you at the windscreen when it misfires or does it feel like an early rev limiter? Did it get worse when you upped the boost?

vessy

Green filter fitted Maf lovely and clean, also fitted known good item with no change.

Seems maybe a little worse since boost has been upped, it isn't a violent hesitation, you just feel the car kick and also hear it from the manifold area. I guess it could be fuel related however we never see any knock activity when it does it, i would have thought if it was a fuel starvation problem we would get serious det before the misfire?

Would i be likely to induce more problems by fitting a colder plug? Don't know why but i just seem to worry about the step from 6's to 7's

DannyBoy007

iTrader: (7)

I used to get a misfire on my My99 uk turbo, it would only misfire around 70-80 when giving it some beans. Turned out to be a hair line crack in number 4 plug, As I was changing them anyhow I changed from 6b's to 7b's, haven't had a problem since.

This was with a K&N induction kit, full decat and remap.

merlin24

iTrader: (1)

If the "rev counter" jumps round,could well be an electrical/ignition problem.
Any corroded harness connectors under the bonnet ??
Have you got good earths to the battery and engine??

vessy

I too thought an electrical problem, The rev gauge is fed from the ECU and the ECU gets rev speed from i think a mixture of cam and crank sensor (never had this confirmed) This would explaine the misfire as the ECU wouldn't know timing, but i have no CEL for either sensor.

All connections look good, the only thing i havent done is continuity check the wiring from the sensors to the ecu, going to try this today. All grounds are good, i've done power checks to the coils and the fuel pump, again these are all good with minimal voltage drop.

I have checked the plugs and they look ok, i don't get any hesitation during cruise or power until i get above 6k, the only other thing i have noticed a few times is ignition noise heard through the radio, perhaps a screening problem with the sensor wiring?

What problems do you usually see if plugs are getting too hot?

vessy

Wiring all checks out OK, continuity checks to each sensor good, shield checked and good to ground, insulation checks carried out between signal wires and ground/shield and no break through, both sensors checked at 2k ohms. Now i'm stumped

classic_sti

mines does the same mate i think its the rev limiter kicking in too early?
mine does it around 6k when it should be 7k ish.
getting mine rolling roaded tomorrow to try sort the prob out.

vessy

Don't think it's rev limiter as the car will still pull through it, although not as quick, rev limiter cuts fuel not ignition so a misfire wouldn't happen, let me know what the rolling road guys think.

classic_sti

took it today the suspected reason for the miss fire was because of worn coil packs they didnt have any in stock..i have since replaced them with fully tested and working coils off another subaru..but ive still got the problem
does yours go passed the miss fire then?
because mine wont go passed 5.5k 6k! its doing my head in

merlin24

iTrader: (1)

Have you had any work/done any work on the car before the misfire
started - might narrow it down a bit.
I have known a few badly fitted alarms/immobilisers causing the car
to misfire and cut out randomly.

classic_sti

mines been like this since i bought it,i only noticed after a few days of owning her, i took it easy on the test drive and after the sale i didnt really give it some for a couple of days..
( wanted to get used to it first its my first scoob) LOL
ive had no work done..its exactly how i got it

vessy

Sounds similar then, coil packs not fixing it!!

I was the same in that i took it easy at first, not reving too high, then once i had serviced the car including spark plugs I felt more comfy opening her up, then i found the problem, everything has been changed since bar the plugs, as mine did it when the engine was standard i don't suspect it's due to being 6b's not 7's.

Mine will pull through as it's more of a fast intermittent misfire, not a constant one that stops all power, we datalogged the car and it showed no knock when it happend, but then on the next pull it didn't do it, where as now it's everytime the revs are high.

I'm still suspecting the cam sensor as this is the only thing i haven't changed, but at £100 i'm not going to throw money at it without proving something, £250 on coil packs was enough hurt.

Going to find a way of monitoring the cam signal whilst driving, i'll let you know if i manage this!

Did the guys at the rolling road check AFR? could be your MAF palying up if you can't get through it.

Anyone got a spare cam sensor i could borrow?

classic_sti

hi, they did a diagnostic and there was no error codes..
would i need to do a different error check for the maf?
cheers bud

vessy

No, error codes would show a serious failure of the MAF, try giving it a clean with carb cleaner, see if it improves things, could just be undereading.

Guess they didn't do an Air/Fuel mesure?

classic_sti

how do i do that ? dont even know where the maf is lol is it the plug near the airbox?
i dont think they did a air/fuel measure. so could this be my problem?
thanks again pal
sorry for bringing my car up on your thread!
your as desperate to sort yours as i am with mine

vessy

No worries, were all here to fix the same problem, hopefully!

MAF is just after the airbox like you say, have to remove it completely and clean the element inside, just be very careful not to touch it, just spray it.

What power did it make out of interest?

classic_sti

ok thanks i will try that
my car has a induction kit on it aswel could this be anything to do with it?

as for the rolling road they didnt do it because of leak from the cat gasket..need to get that sorted aswel now

crusher

vessy, if I were you I'd try another set of new plugs before anything else. Have seen brand new sets have one plug cause a problem with glazing over...causes misfire...and cleaning plug doesn't help...

vessy

Thanks Crusher, think i'm going to do that, prob fit 7's as were already around 50 over the standard bhp.

Still going to have a look at the cam signal, on a mission now

vessy

Yes, if it's an oiled filter then this is a common problem. Give it a clean, hopefully you'll have a new beast, if not at least you rule out the chance of it running lean and causing you £££££££££££

classic_sti

cleaned the MAF today and still no luck
im unsure if its a oil filled induction kit?
do you think im better putting it back to standard then..standard box-filter

vessy

An induction kit shouldn't cause it, but you could always put the standard air box on to check, I know it's time consuming but these problems normally are, least you can eliminate one more thing. Have you changed/checked the plugs? Gapping the plugs is critical to 0.7mm, fresh out of the box they can be anything up to 1mm gap!

It's always time consuming doing this sort of thing but elimination is the only sure way if you have no CEL to help, check all your boost pipework as well, especially the components on the R/H suspension strut, this is where the pressure sensor is for the ECU. If you still can't find anything obvious then get the gasket fixed and rolling road the car, get them to check fueling.

classic_sti

plugs have been changed to ngk platinums..the problem was there when the old plugs were fitted aswel.
thanks alot mate really apreciate your help! ill check the gaps..
good luck with yours

Delboy2

Classic sti - does your missfire occur in every gear or only high gears (3rd 4th & 5th)?

Cheers

classic_sti

every gear

Delboy2

classic sti - you have already done the plugs & coilpacks, try the earthing modification as early scoobs are notorious for having bad earths. Another 'port' of call would be the fuel pump as they can be problematic after 70-80K (get a little tired) an AFR plot from a wideband or a Dyno would confirm.
Vessy - If you have a chip fitted it would be worth fitting an uprated pump especially if over 70-80k and a uprated regulator for the reasons above, plus have you both tried closing the gaps on the plugs to either 0.6mm or 0.5mm?

Cheers

coulty

hey del

could also have a couple of unseated valves that i had on my sti2 (unbeknown to me). I had misfire as the MAF voltage was peaking (coincidence) that turned out in the end to be the valves.

Stuart